Tuesday, December 21, 2010

Mammal watching has never achieved the popularity of bird watching for at least one reason: most mammals are nocturnal. Not only are most of them small and brown, but you can’t even see them! Mammalogists survey mammals by trapping them, netting them, looking for their tracks and scat, etc. Their survey methods don’t usually include walking around with a pair of binoculars on a nice, sunny day in spring.

But there are exceptions. Some mammals are much more visible than others, primarily because they are diurnal. These include many of the large grazing and browsing hoofed mammals (ungulates), the cute pikas of western mountains, and the squirrels. The Pacific Northwest is abundantly provided with squirrels, encompassing the taxonomic range of the squirrel family: flying squirrels, tree squirrels, ground squirrels, marmots, and chipmunks.

Chipmunks come close to being birdwatchers’ mammals. They are active during the day, with an emphasis on the “active,” they are brightly marked, they are territorial, they vocalize frequently, and they come readily to bird feeders. They vary from very shy to very inquisitive, even tame where they encounter people regularly. They are still basically brown, but their conspicuous stripes make them easily recognizable as chipmunks.

These small squirrels are usually associated with rock piles and fallen logs, where they nest. They forage on the ground and in shrubs, sometimes ascending well up into the trees. Hyperactivity describes them best, as they move jerkily along with tail cocked up into the air. When disturbed, they dart into cover, appearing some distance away for another look at the disturbance.

Basically seed eaters, chipmunks will take anything that comes along, including fruits, fungi, and arthropods. They are accomplished nest robbers. taking bird eggs whenever they can find them. During the fall, they busily gather seeds in cheek pouches and cache them in their protected nests. They can then hole up for the winter and feast on these caches without leaving their protected shelter. Caches can contain tens of thousands of seeds.

Most western states have several species of chipmunks; Washington has four. The most common and widespread species in Washington is the Yellow-pine Chipmunk (Tamias amoenus), so named because it is common in the ponderosa (or yellow) pine zone east of the Cascade Mountains crest. Absent from the dense forest of the western lowlands and mid elevations in the mountains, it is again common in the subalpine-alpine zone of the Cascades and Olympics. It is easily seen by hikers in the high country and drivers through almost any of the interior national forests. It is at home in trees, ascending high into pines to forage for the seeds.

The Red-tailed Chipmunk (Tamias ruficaudus) looks about like the Yellow-pine but is slightly larger and longer tailed, and the tail is more intense reddish below. It occurs in the mountains of far northeastern Washington, in Stevens, Pend Oreille, and northern Spokane counties. Its habitat zone is the montane conifer forest and open subalpine zone above that, mostly above the elevation range of the Yellow-pine.

This species would not have been separated from the Yellow-pine but for its copulatory organ. Rodents have a bony structure in the penis called the baculum, and this structure differs among different species of chipmunks. That of the Red-tailed is distinctly longer than that of the Yellow-pine. I have not read of any structural characteristics that differentiated the females!

The largest Washington chipmunk is the Townsend’s (Tamias townsendii), restricted to the forested western lowlands and similar dense habitats up to treeline in the Olympics and Cascades. It occurs in both forested and open (e.g., clear cuts) microhabitats. It is not found in the more open ponderosa pine woodlands below the wet conifer forests on the east side. In addition to being larger and darker, not as brightly marked, it differs from all the other species in not having a clearly defined dark stripe extending from nose to eye. This and the Yellow-pine often occur together in ecotones between open alpine or ponderosa pine habitat on one side and dense conifer forest on the other. Washington Pass is one such location.

Finally, the Least Chipmunk (Tamias minimus) is restricted to sagebrush habitats in the southern part of the Columbia Basin. It is a smaller species, generally paler and grayer than the others, with the back stripes brown instead of blackish and very little reddish or brown color anywhere. It overlaps with Yellow-pine where sagebrush, grassland, and ponderosa pine come together. Least Chipmunks occur at higher densities than the other species, and one place to see this is at the Ryegrass rest stop east of Ellensburg on eastbound I-90. It is full of Least Chipmunks most of the year, gathering by the dozens at the feast of sunflower seeds put out by DOT employees.

There is also a pair of chipmunk lookalikes in Washington. The Cascade Golden-mantled Ground Squirrel (Spermophilus saturatus) is found throughout the Cascades, in both semiopen conifer forest and alpine meadows. The Golden-mantled Ground Squirrel (Spermophilus lateralis) occurs in similar habitats in the Blue Mountains and, less commonly, the mountain ranges east of the Okanogan River. Both are larger than chipmunks, with an unstriped golden-orange head. Most ground squirrels eat leaves rather than seeds, but these species are more chipmunk-like in their diet.

Friday, December 17, 2010

Many kinds of birds dive for a living. Not from a diving board, but from the air or the water surface. Some of these birds fly over the water, see potential prey, and dive from the air to attempt capture. These birds are called plunge divers. Gulls plunge into the water to about their own body length and retrieve prey from near the surface. Terns, some pelicans, tropicbirds, and boobies dive from above the surface, the first three penetrating farther into the water column than the gulls do. Boobies (and their close relatives the gannets) penetrate well below the surface and actively chase fish underwater.

Many other birds dive from the water surface, including loons, grebes, cormorants, alcids (puffins and their relatives), diving-petrels, some shearwaters, coots, and many ducks. In this discussion let’s look at this group, so-called surface divers.

All diving birds have feet that are modified for swimming at the surface, and these same feet serve them well for underwater propulsion. The typical swimming foot is that of a duck, with the three forward toes joined by webs. The hind toe is much reduced. Among the diving birds, these webbed feet also characterize loons, gulls, terns, shearwaters, diving-petrels, and alcids (this last group lacks a hind toe).

A variation on this is to have the hind toe lengthened and all four toes connected by webs. This characterizes cormorants, pelicans, boobies, and tropicbirds. Finally, instead of webs, some birds have each of the toes, including the hind one, provided with large, flat lobes that are equally efficient in propelling the bird forward. Divers with lobed toes include grebes and coots.

Surface divers vary quite a bit in how they dive and how they locomote under water. Most of them just put their head down, slide under the surface, and propel themselves downward. Although the feet stroke alternately while swimming on the surface, when underwater they stroke in unison, like a pair of oars, and they are held out to either side. This must use different sets of muscles than those used for swimming on the surface. Smaller birds such as grebes, coots, and small cormorants may jump up into the air to enter the water with more momentum.

One group of birds exhibits a real variation in this theme. The alcids are wing-propelled surface divers, using their wings to swim just as if they were flying underwater. As they go below the surface, you can see their wings already open as their means of propulsion. In the guillemots, which feed on bottom fish, the feet are used along with the wings, but in murres and puffins and others that feed on midwater fish and krill, they are held behind and not used at all. The southern-hemisphere diving-petrels, related to true petrels, also use this method of propulsion, as do penguins. Not able to fly, penguins are the most highly modified birds for underwater living.

Scoters and some other sea ducks such as Long-tailed Ducks open their wings as they dive, easily seen. They may use them as diving planes underwater or may actually flap them just as alcids do. For the most part, diving birds surface just by stopping their underwater propulsion and, like a cork, popping back up to the surface. They go headfirst, the most streamlined way to go. Alcids sometimes swim actively upward and penguins always do.

Although you would think that fish are the fastest swimmers in the sea, the most amazing thing about diving birds to me is that they can swim faster than the fish, presumably a necessity if they are to catch them! Both animals streak through the water, and just like a smaller bird trying to escape from a hawk, the fish may or may not escape.

Still photos of birds swimming underwater are very hard to come by, although YouTube and other such online video sites show a variety of birds swimming underwater, very often misidentified (grebes and alcids called “ducks”). Notwithstanding these few videos, we have much to learn about how diving birds forage underwater.

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About the Slater Museum

Our goals are to preserve and provide a collection of specimens to be used for research and education. Located in Tacoma, Washington, the Slater Museum is one of the region's significant repositories for bird, mammal, reptile, amphibian and plant specimens from the Pacific Northwest. In addition, we strive to educate the local community about nature and about the value of museums.